STAART CENTER: Individual differences in response to treatments of autism spectrum disorders (ASDs) present a serious problem in choice of treatment. If we could predict in advance which children would benefit from the available interventions and which would not, children could be matched to treatments. On the other hand, individual differences in response to treatment may represent an opportunity for studies of the etiology of autism. Responders and non-responders are likely to represent different subsets of the spectrum that may be genetic in origin. Along with other phenotypic characteristics of children with ASDs, response to treatment is a dimension that deserves investigation as a possible way to stratify the spectrum for genetic studies. We propose studies of children's response to two of the most commonly used treatments of ASDs: early intensive behavioral intervention (Project I) and the gluten-free, casein-free diet (Project II). Each treatment project is accompanied by a related neurobiological investigation. Project III is an examination of the neurobiology of facial expression and imitation, which are important in the behavioral interventions under study in Project I. Project IV is an investigation of the sense of taste in both humans and animals, based on preliminary evidence that children with ASDs have dysfunction in this modality. It addresses dietary issues broader than the specific diet under study in Project II. Each Project has a genetic component, to explore the relationship of six suspected candidate genes to treatment response and other phenotypic characteristics of children with ASDs. A Genetics Core will provide the molecular testing for these studies. Each Project will use an Assessment and Records Core for characterizing participants and/or identifying and recruiting appropriate participants. An Administrative core will oversee the program, providing budgetary oversight, internal and external review of progress, statistical services, interactions with the community, and regular interactions between investigators. This proposal takes advantage of an unusual environment. The availability of intensive early behavioral intervention at public expense facilitates treatment studies. A large population of children with ASDs and families anxious to participate in research facilitate recruitment. The presence of a biologically-oriented CPEA complements the Projects of the STAART Center.